Abstract
Chronic lung infections are associated with increased morbidity and mortality for individuals with underlying respiratory conditions such as cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD). The process of chronic colonisation allows pathogens to adapt over time to cope with changing selection pressures, co-infecting species and antimicrobial therapies. These adaptations can occur due to environmental pressures in the lung such as inflammatory responses, hypoxia, nutrient deficiency, osmolarity, low pH and antibiotic therapies. Phenotypic adaptations in bacterial pathogens from acute to chronic infection include, but are not limited to, antibiotic resistance, exopolysaccharide production (mucoidy), loss in motility, formation of small colony variants, increased mutation rate, quorum sensing and altered production of virulence factors associated with chronic infection. The evolution of Pseudomonas aeruginosa during chronic lung infection has been widely studied. More recently, the adaptations that other chronically colonising respiratory pathogens, including Staphylococcus aureus, Burkholderia cepacia complex and Haemophilus influenzae undergo during chronic infection have also been investigated. This review aims to examine the adaptations utilised by different bacterial pathogens to aid in their evolution from acute to chronic pathogens of the immunocompromised lung including CF and COPD.
Highlights
The respiratory tract is the first point of contact in the lungs for pollutants and microorganisms, with, on average, 10,000 L of air inhaled per person per day
Chronic lung infections are associated with increased morbidity and mortality for individuals with underlying pulmonary disorders, for cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD) patients
The pathogenesis and adaptation mechanisms utilised by Gram positive and Gram negative bacteria during chronic lung infection involves numerous complex and diverse virulence factors
Summary
The respiratory tract is the first point of contact in the lungs for pollutants and microorganisms, with, on average, 10,000 L of air inhaled per person per day. The resident microbiome will depend on geography, climate and other environmental conditions [5] Both cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD) are characterised by airway inflammation, altered mucus production and diminished mucocillary clearance. Other pathogens associated with CF lung infection include, Haemophilus influenzae, Stenotrophomonas maltophilia, Achromobacter xyloxidans, genus Pandoraea and Gram positive species including S. aureus, and Streptococci as recently reviewed [11]. These lung pathogens chronically colonise the CF lung contributing to gradual but unrelenting decline in pulmonary function and tissue damage [12]. P. aeruginosa, which chronically colonises the CF lung, is not frequently associated with persistence in COPD patients [14]
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